This invention relates to carbon black coated with a compatibilizing agent to enhance its dispersibility in a melt of a plastic material. The invention further relates to a method for enhancing the dispersion of carbon black into a melt of a plastic material. The invention further relates to a process for incorporating carbon black in a plastic foam structure.
Carbon black is known as an infrared radiation absorber and reflector, and has been commercially employed in insulative foam structures to reduce thermal conductivity. Extensive teachings of that use are seen in U.S. Pat. No. 4,795,763 and WO 90/06339, both of which are incorporated by reference herein.
Problems with incorporating carbon black in insulative foam structures include processing problems such as poor dispersion and high process pressures and product quality problems such as poor cellular structure and poor skin quality.
Carbon black does not typically disperse well in a polymer melt or polymer gel of the melt with a blowing agent. Adequate dispersion may require pre-compounding of the carbon black in the base polymer prior to manufacturing the foam structure. Pre-compounding is expensive, and the carbon black still may not be sufficiently dispersed. Adequate dispersion is needed to achieve maximum efficiency in reducing thermal conductivity in the foam structure and to ensure desirably low levels of water and water vapor permeability through the structure.
High process pressures may result from operating process equipment such as extruders at high operating rates to ensure adequate dispersion of the carbon black.
Poor skin quality and poor cellular structure may result from making extruded foam structures with carbon black. If poorly dispersed, carbon black may negatively impact skin quality and cellular structure of the foam structure as it exits the extrusion die. Poor cellular structure may take the form of irregular or uncontrolled cell size, or large voids or abscesses.
One means of enhancing dispersion of carbon in a process for making a foam structure is seen in U.S. Pat. Nos. 5,149,722, 5,137,190, and 5,192,607. In a process for making a polyisocyanurate or a polyurethane foam structure, a capped polyoxyalkylene compound is added to one of the reactive components. A disadvantage of such means is that relatively large amounts of the polyoxyalkylene compound must often be employed to achieve a desirable degree of dispersion. Large amounts are expensive, and may impact critical physical properties of the end product foam structure. Further, the enhancement is taught only with respect to processes for making polyurethane and polyisocyanurate foam structures.
It would be desirable to find a means for enhancing dispersion of carbon black in melts of plastic materials. It would be further desirable to find a means for enhancing dispersion of carbon black in plastic foaming processes. It would be further desirable if skin quality and cellular structure could be improved when using carbon black in extrusion foaming processes.